Health insurance is widely regarded as essential for financing the production of good health, but is insurance always beneficial for out health? Ex ante moral hazard may induce individuals with insurance to engage in behaviors that they otherwise would not undertake in the absence of insurance. Using data from the 1993�2002 Behavioral Risk Factor Surveillance System, we attempt to isolate the effects of ex ante moral hazard to determine the potential consequence of having health insurance on measures of body weight. In our analyses, we control for a variety of confounding factors that may influence body weight and address the endogenous nature of health insurance. Our results suggest that having insurance is associated with higher body mass but not the probability of being obese.